THE WATTHOUR METER - ITS ROLE IN THE DISTRIBUTION UTILITY

THE ELECTRIC UTILITY AND THE COMMUNITY

THE ELECTRIC COMPANY and the community which it serves are permanently interdependent. An electric company, by the nature of its business, cannot pick up its generating plant, transmission, or distribution system and move to some other community.

It is firmly rooted where it is located. Its progress depends to a large extent upon the progress of the area it serves; also, it depends upon the respect and active support of its customers. It makes good sense for the electric company to work cordially and cooperatively with its customers toward the improvement of economic and civic conditions.

Because of this, the meter reader or meter technician must be aware that they represent the “Company” when calling on a customer’s home or business. What the electric company sells and/or delivers has become essential to the point that loss of electric power causes more than inconvenience; it can mean real hardship, even tragedy.

In addition, large quantities of electricity cannot be produced and stored and so must be immediately available in sufficient quantities upon demand. What this means is that we sell and/or deliver not only the commodity of electric energy but a very valuable service as well.

The service performed by the electric company and its employees should be so well done that every member of the company and the community can be proud of it.

THE GENERIC WATTHOUR METER
There are a number of ways to implement a watthour meter, but all approaches require power to be measured, accumulated, and the results stored and displayed. As such, voltage and current for each electrical phase must be sensed (or approximated), voltage and current for each electrical phase must be multiplied, the resultant power must be accumulated, and the accumulated watthours must be stored and displayed.

For the electricity provider, the electricity meter (the watthour meter) is the cash register. As such, the meter must be very accurate and reliable over a variety of environmental conditions, and the meter performance must be certifiable to the energy provider, consumer, and any involved regulatory agencies.

A major challenge for the watthour meter manufacturer is to perform these functions economically. Each watthour meter approach has tradeoffs that are balanced by the meter manufacturer to meet the perceived market needs. The best approach depends on how the user values the tradeoffs.

Because of the care taken in their design and manufacture, and because of the long-wearing qualities of the materials used in them, modern watthour meters normally remain accurate for extended periods of time without periodic maintenance or testing.

Probably no commodity available for general use today is so accurately measured as electricity.

Important Terms used in metering:

Constant,Watthour—
(a) For an electromechanical meter (Kh): The number of watthours represented by one revolution of the disk, determined by the design of the meter and not normally changed. Also called Disk Constant.

(b) For a solid-state meter (Kh or Kt): The number of watthours represented by one increment (pulse period) of serial data. Example: Kh or Kt = 1.8 watthours/pulse.

Registration—The registration of the meter is equal to the product of the register reading and the register constant. The registration during a given period of time is equal to the product of the register constant and the difference between the register readings at the beginning and the end of the period.

Watthour Meter—An electricity meter that measures and registers the integral, with respect to time, of the active power of the circuit in which it is connected. This power integral is the energy delivered to the circuit during the interval over which the integration extends, and the unit in which it is measured is usually the kilowatthour.

Watthour Meter Portable Standard—A special watthour meter used as the reference for tests of other meters. The standard has multiple current and voltage coils or electronic equivalents, so a single unit may be used in the field or in the shop for tests of any normally rated meter.

The portable standard watthour meter is designed and constructed to provide better accuracy and stability than would normally be required in customer meters.

The rotating standard has an electromechanical dial rotating at a specified watthour per revolution; the solid-state standard has a digital display of 1 watthour per revolution, or, essentially, a measured watthour.